The present invention relates to a water-capturing or drying agent capable of absorbing moisture within a sealed container housing electronic components therein for a long period of time. In particular to a thin field light emission device which is capable of mass-producing the thin field emission device with high reliability and is not susceptible to moisture and oxygen for a long period of time and maintains stable emission by using the water-capturing or drying agent.
In general, a field light emission device enclosed in a sealed container comprises a luminescent layer interposed between a pair of electrodes in the hermetically sealed container. There are two types of field light emission devices, one is an organic EL device comprising a luminescent layer composed of mainly fluorescent organic compound, and the other is an inorganic EL device comprising a luminescent layer composed of mainly an inorganic phosphor.
The organic EL device composed of the fluorescent organic compound has a luminescent part which is a laminate formed by interposing an EL layer containing the fluorescent organic compound between an anode and a cathode. Such an organic EL device is a self-luminescent device which injects a hole and an electron into a thin film containing the fluorescent organic compound to re-combine each other to generate an exciton and utilizes emission of fluorescence/phosphorescence at the time of deactivation of the exciton.
The inorganic EL device which is composed of the inorganic phosphor comprises generally a lower electrode, an inorganic phosphor, a dielectric material and an upper electrode which are laminated on the top surface of a substrate in that order and emits light by applying high-frequency voltage between the electrodes.
The organic and inorganic EL devices are hermetically sealed in the container maintaining ultramicromoisture. Since the micromoisture has an adverse effect on characteristics of the EL device, a drying agent is generally placed in the sealed container in order to absorb and/or remove moisture therefrom. The drying agent is frequently referred to as a water-capturing agent, because it captures and absorbs moisture in the EL device housed in the sealed container. Accordingly, the drying agent used in the EL device in the present invention is hereinafter referred to as a water-capturing or drying agent. Embodiments of the water-capturing or drying agent used in the organic EL device will be explained hereinafter.
Since a functional part of the organic EL device is extremely susceptible to damage from moisture, the functional part is hermetically sealed in a container composed of glass or metal so as not to be exposed to the outside. More specifically, the functional part is laminated on a substrate such as glass, over which a sealing cap made of glass or metal is put on the substrate to be bonded to the substrate, thereby confining the functional part in a hermetically sealed container composed of the substrate and the sealing cap. Then, a water-capturing agent such as barium oxide (BaO) or calcium oxide (CaO) is put into the EL device to capture water so that moisture attached to the functional part or being present in an atmosphere inside the hermetically sealed container or permeating into the inside from the hermetically sealed container through a sealing section can be captured as disclosed in Japanese Patent Publication Hei 9-148066.
FIG. 1 is a cross section showing the structure of an example of the organic EL device. The anode 2 made of a transparent conductive film such as ITO (indium tin oxide), the organic layer 3 containing organic EL medium, and the cathode 4 are laminated on the substrate 1 made of glass in that order to form the functional part. Then, the sealing cap 5 formed of metal is put over the EL device to cover the EL device and bonded to the substrate 1 with the adhesive 6 to form the hermetically sealed container. The anode 2 and the cathode 4 penetrate hermetically through the sealing section of the hermetically sealed container to be lead to the outside so as to drive the functional part. A recess 7 is formed at the sealing cap 5, in which powder BaO is filled as the water-capturing or drying agent 8 and sealed with a water permeable film. In this example, the light emitted from the organic layer 3 is passed through the anode 2 and the substrate 1 of glass in the downward direction in FIG. 1.
FIG. 2 is a cross section showing the structure of another example of the organic EL device, in which a recess 10 is formed by countersinking process, such as sandblast, etching, and the like, on one side of the glass plate opposite to the functional part instead of the sealing cap made of metal in FIG. 1. The water-capturing or drying agent 12 made by packing CaO powder with a water-permeable agent or seal-shaped water-capturing agent is adhered to the inner surface of the recess 10 of the sealing substrate 11 made of glass. The rest of the structure is similar to that of shown in FIG. 1. In this example, the light emitted from the organic layer 3 is passed through the anode 2 and the substrate 1 in the downward direction in FIG. 2. It is possible to make the light emitted from the organic layer 3 pass through the cathode 4 and the sealing substrate 11, as disclosed in Japanese Patent Publication 2002-33187 and Japanese Patent Publication 2003-144830, if a light-transmissible cathode and a light-transmissible water-capturing or drying agent. For example, a simple compound of an organometallic compound illustrated by the chemical formula (1) may be used:
In chemical formula (1), R1, R2, and R3 are a hydrogen atom or an alkyl group, aryl group, cycloalkyl group, or heterocyclic ring group having one or more carbon atoms; one or more hydrogen atoms in each of groups may be substituted for a halogen atom; R1, R2, and R3 may be from different groups, may be from the same group, may be bonded to each other, or may be a polymer, and M is a trivalent metal atom.
FIG. 3 is a cross section showing a top emission-type organic EL device using the sealing substrate 13 made of glass in the shape of a plate instead of the sealing substrate 5 made of metal shown in FIG. 1 and the sealing substrate 11 made of glass. The anode 2, the organic layer 3, and the light-transmissible cathode 14 are laminated in that order on the base substrate 1 made of glass. The inorganic water-barrier layer 15 is laminated thereon to form the functional part to which the sealing substrate 13 is bonded via an adhesive layer. Thus, a complete solid sealing structure is formed having no space between the base substrate 1 and the sealing substrate 13. UV-light curable sealing agent 17, for example, epoxy sealing agent is placed onto the periphery of the adhesive layer 16 to seal the adhesive layer 16 between the base substrate 1 and the sealing substrate 13. In this example, the light emitted from the organic layer 3 is passed through the cathode 14, the adhesive layer 16, and the sealing substrate 13 in the upward direction in FIG. 3 as disclosed in Japanese Patent Publication 2002-231443.
In the organic EL device shown in FIG. 1, the recess 7 is formed on the sealing cap 5 for sealing the functional part on the base substrate 1 by a press molding process. In the organic EL device shown in FIG. 2, the recess 10 is formed on the sealing substrate 11 by a countersinking process. The recess 7 or 10 is filled with BaO or CaO powder as a drying agent for capturing water in the organic EL device. A water-capturing or drying agent in the shape of a sheet formed of the BaO or CaO powder may be applied to the recess 7 or 10. However, if the recess 7 or 10 is filled with a required amount of the water-capturing agent powder, the thickness thereof becomes 0.2 mm at the minimum, and the recess 7 or 10 must have at least 0.3 to 0.5 mm in thickness. As a result, the thickness of the sealing substrate 11 or the sealing cap 5 becomes large, and the thickness of the organic EL device as a whole becomes thick.
BaO and CaO used for a water-capturing or drying agent in the EL device are liable to scatter, because BaO and CaO are powder. Thus, it is necessary to inhibit the scattering thereof when sealing them into the recess 7 or 10. This creates such a problem that workability is bad, automation is difficult, and the adhesion strength of the seal lowers if the BaO or CaO powder is adhered to the area to be coated.
In the organic EL device shown in FIG. 3, TFT circuit is formed on the surface of the base substrate 1 on the side of the anode 2, on which the functional part is laminated. Consequently, the light emitted from the organic layer 3 of the functional part can not pass through the anode, but instead passes through the cathode 14 via the sealing substrate 13 as described above. The BaO or CaO powder as a water-capturing agent or a water-capturing agent in the shape of sheet using the BaO or CaO powder is not transparent. Thus, the water-capturing or drying agent can not be placed on the cathode 14 through which light passes in the organic EL device shown in FIG. 3.
On the other hand, improved water-capturing performance can be expected when a solution of the single compound of the light transmissible organometallic compound, for example, shown in chemical formula (1) of Japanese Patent Publication 2002-33187 dissolved in an organic solvent, is applied as a water-capturing or drying agent on the inner surface of the recess 10 formed in the sealing substrate 11 by countersinking.
Inventors of the present invention have reviewed the molecular structure of a single compound of the conventional water-capturing or drying agent shown in the chemical formula (1) in order to improve the water-capturing effect. Inventors of the present invention have inferred that the water-capturing effect can be improved by bonding the water-capturing or drying agent shown in the chemical formula (1) with an oxygen molecule to make the reaction with water easy to occur.
The present invention improves the reliability of the EL device by using as a water-capturing or drying agent an organometallic compound illustrated by the chemical formula (5):
wherein M is a trivalent metal atom.
By dimerizing the organometallic compound illustrated by the chemical formula (1) as shown in the formula (5) to form a molecular structure of dimer, torsion is generated in the molecule and the molecule of water becomes easy to attack an oxygen atom at the crosslinking section of the dimer. On the other hand, the water-capturing or drying agent of the prior art shown in chemical formula (1) has a hydrophobic substituent in the single compound. Thus, a water molecule is hard to approach it. Accordingly, the reaction of the conventional water-caturing or drying agent with water is hard to occur, thereby decreasing the water-capturing or drying performance.
A reaction formula with water is shown in reaction formula (6):

The dimer compound illustrated by the chemical formula (5) reacts with water to form a monomer of six-membered ring shown in the chemical formula (1) as shown in the reaction formula (A) of the above chemical formula (6). As a result, the compound in the chemical formula (5) absorbs water and acts as a water-capturing or drying agent. In the chemical formula, M is a trivalent metal atom. Then, the monomer of six-membered ring reacts with water as shown in the reaction formula (B) of the above chemical formula (6). After such reaction proceeds completely, hydroxide of trivalent metal M (OH)3 is generated. As a result, the compound absorbs water and acts as a water-capturing or drying agent. Similarly, the reaction with trimer, tetramer and pentamer, as well as a polymer of the organometallic compound shown by chemical formula (1) proceeds and water-capturing or drying effect increases.
An example of the trimer is shown in chemical formula (7).
wherein M is a trivalent metal atom.
An example of the tetramer is shown in chemical formula (8).
wherein M is a trivalent metal atom.
Another example of the tetramer is shown in chemical formula (9).
wherein M is a trivalent metal atom.
By dimerizing, trimerizing, tetramerizing, pentamerizing or polymerizing the molecular structure in such a manner as described above, torsion is generated in a molecule and the molecule of water becomes easy to attack an oxygen atom at crosslinked section. On the other hand, the water-capturing or drying agent of prior art shown in chemical formula (1) has a hydrophobic substituent. Thus, a water molecule is hard to approach. Accordingly, the reaction of the conventional water-capturing or drying agent with water is hard to occur, and water-capturing performance is decreased.
In addition to the compounds shown by the above chemical formulae (2) to (4), various kinds of polymers obtained by bonding a plurality of organometallic compounds having a trivalent metal atom M with an oxygen atom have torsion in their molecules. A water molecule is, therefore, easy to attack an oxygen atom at a crosslinked section to impart the water-absorbing effect to such various kinds of polymers. The metal atom M may be Al, Ga, In, La, Y and other trivalent metal atom.
Examples of compounds illustrated by chemical formula (1) in which R1, R2 and R3 are substituted are those illustrated by the following chemical formulae (10), (11) and (12).
wherein M is a trivalent metal atom.
wherein M is a trivalent metal atom.
wherein M is a trivalent metal atom.
In the formulae, R is one selected from the group consisting of an alkyl group, aryl group, cycloalkyl group, heterocyclic group. Alkyl group may be exemplified by a methyl group, ethyl group, propyl group, butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group, heneicosyl group, docosyl group, and the like.
Aryl group may be exemplified by a phenyl group, tolyl group, 4-cyanophenyl group, biphenyl group, o,m,p-terphenyl group, naphthyl group, anthranyl group, phenanthrenyl group, fluorenyl group, 9-phenylanthranyl group, 9,10-diphenylanthranyl group, pyrenyl group, and the like.
Cycloalkyl group may be a cyclopentyl group, cyclohexyl group, norbornane group, adamantane group, 4-methylcyclohexyl group, 4-cyanocyclohexyl group and the like.
Examples of heterocyclic group may be a pyrrole group, pyrroline group, pyrazole group, pyrazoline group, imidazole group, triazole group, pyridine group, pyridazine group, pyrimidine group, pyrazine group, triazine group, indole group, benzimidazole group, purine group, quinoline group, isoquinoline group, cinorin group, quinoxaline group, benzquinoline group, fluorenone group, dicyanofluorenone group, carbazole group, oxazole group, oxadiazole group, thiazole group, thiadiazole group, benzoxazole group, benzothiazole group, benzotriazole group, bisbenzooxazole group, bisbenzothiazole group, bisbenzoimidazole group and the like.